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</head>
<body class="article">
<div id="header">
<h1>Picocli 2.0: 以少求多</h1>
<div class="details">
<span id="revnumber">version 4.7.6</span>
</div>
</div>
<div id="content">
<div class="sect1">
<h2 id="_简介">简介</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Picocli是一个单文件命令行解析框架，它允许您创建命令行应用而几乎不需要代码。使用 <code>@Option</code> 或 <code>@Parameters</code>
在您的应用中注释字段，Picocli将分别使用命令行选项和位置参数填充这些字段。例如:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="java"><span class="annotation">@Command</span>(name = <span class="string"><span class="delimiter">&quot;</span><span class="content">Greet</span><span class="delimiter">&quot;</span></span>, header = <span class="string"><span class="delimiter">&quot;</span><span class="content">%n@|green Hello world demo|@</span><span class="delimiter">&quot;</span></span>)
<span class="type">class</span> <span class="class">Greet</span> <span class="directive">implements</span> <span class="predefined-type">Runnable</span> {

  <span class="annotation">@Option</span>(names = {<span class="string"><span class="delimiter">&quot;</span><span class="content">-u</span><span class="delimiter">&quot;</span></span>, <span class="string"><span class="delimiter">&quot;</span><span class="content">--user</span><span class="delimiter">&quot;</span></span>}, required = <span class="predefined-constant">true</span>, description = <span class="string"><span class="delimiter">&quot;</span><span class="content">The user name.</span><span class="delimiter">&quot;</span></span>)
  <span class="predefined-type">String</span> userName;

  <span class="directive">public</span> <span class="type">void</span> run() {
    <span class="predefined-type">System</span>.out.println(<span class="string"><span class="delimiter">&quot;</span><span class="content">Hello, </span><span class="delimiter">&quot;</span></span> + userName);
  }

  <span class="directive">public</span> <span class="directive">static</span> <span class="type">void</span> main(<span class="predefined-type">String</span>... args) {
    CommandLine.run(<span class="keyword">new</span> Greet(), <span class="predefined-type">System</span>.err, args);
  }
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>当我们执行这个程序时，Picocli会解析命令行，并在调用 <code>run</code> 方法之前填充 <code>userName</code> 字段:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="bash">$ java Greet -u picocli

Hello, picocli</code></pre>
</div>
</div>
<div class="paragraph">
<p>Picocli采用 <a href="http://picocli.info/#_ansi_colors_and_styles">Ansi颜色和样式</a>生成使用帮助消息。如果我们进行无效输入来运行上面的程序(缺少必须的用户名选项)，
picocli会输出一条错误和使用帮助信息:</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="../images/Greet-screenshot.png" alt="错误信息和使用帮助的屏幕截图"></span></p>
</div>
<div class="paragraph">
<p>Picocli可以生成一个 <a href="http://picocli.info/autocomplete.html">自动补齐</a>脚本，脚本允许最终用户使用
<code>&lt;TAB&gt;</code> 命令行补全，从而来发现哪些选项和子命令可用。您还可能喜欢Picocli对
<a href="http://picocli.info/#_subcommands">子命令</a>和 <a href="http://picocli.info/#_nested_sub_subcommands">嵌套子命令</a>及任何深度子命令的支持。</p>
</div>
<div class="paragraph">
<p><a href="http://picocli.info">用户手册</a>详细描述了picocli的功能。本文重点介绍Picocli 2.0版本中引入的新功能。</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_带位置参数的混合选项">带位置参数的混合选项</h2>
<div class="sectionbody">
<div class="paragraph">
<p>我们对解析器进行了改进，现在位置参数现在可以与命令行上的选项混在一起。</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="../images/whisk.png" alt="whisk"></span></p>
</div>
<div class="paragraph">
<p>以前，位置参数必须紧随选项。
从此版本开始，任何非选项或子命令的命令行参数都将被解释为位置参数。</p>
</div>
<div class="paragraph">
<p>例如：</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="java"><span class="type">class</span> <span class="class">MixDemo</span> <span class="directive">implements</span> <span class="predefined-type">Runnable</span> {
  <span class="annotation">@Option</span>(names = <span class="string"><span class="delimiter">&quot;</span><span class="content">-o</span><span class="delimiter">&quot;</span></span>)
  <span class="predefined-type">List</span>&lt;<span class="predefined-type">String</span>&gt; options;

  <span class="annotation">@Parameters</span>
  <span class="predefined-type">List</span>&lt;<span class="predefined-type">String</span>&gt; positional;

  <span class="directive">public</span> <span class="type">void</span> run() {
    <span class="predefined-type">System</span>.out.println(<span class="string"><span class="delimiter">&quot;</span><span class="content">positional: </span><span class="delimiter">&quot;</span></span> + positional);
    <span class="predefined-type">System</span>.out.println(<span class="string"><span class="delimiter">&quot;</span><span class="content">options   : </span><span class="delimiter">&quot;</span></span> + options);
  }

  <span class="directive">public</span> <span class="directive">static</span> <span class="type">void</span> main(<span class="predefined-type">String</span><span class="type">[]</span> args) {
    CommandLine.run(<span class="keyword">new</span> MixDemo(), <span class="predefined-type">System</span>.err, args);
  }
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>使用选项和位置参数的混合来运行上面的类表明，非选项被认为是位置参数。例如：</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="bash">$ java MixDemo param0 -o AAA param1 param2 -o BBB param3

positional: [param0, param1, param2, param3]
options   : [AAA, BBB]</code></pre>
</div>
</div>
<div class="paragraph">
<p>为了支持具有位置参数的混合选项，已对解析器进行更改。 从 picocl2.0开始，多值选项(数组、列表和映射字段)不再<strong>默认为贪婪的</strong>。
2.0版本详细描述了此变化和其他 <a href="https://github.com/remkop/picocli/releases/tag/v2.0.0#2.0-breaking-changes">潜在的重大变更</a>。</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_发现集合类型">发现集合类型</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Picocli将命令行参数的 <a href="http://picocli.info/#_strongly_typed_everything">自动类型转换</a>执行到带注释字段的类型。命名选项和位置参数都可以是强类型。</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="../images/binoculars.jpg" alt="binoculars"></span></p>
</div>
<div class="paragraph">
<p>在v2.0之前，picocli需要使用 <code>type</code> 属性对 <code>Collection</code> 和 <code>Map</code> 字段进行注释，
以便能够进行类型转换。对于具有其他类型的字段，像数组字段和单值字段，如 <code>int</code> 或 <code>java.io.File</code> 字段，picocli自动从字段类型中检测目标类型，但是集合和映射需要更详细的注释。例如：</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="java"><span class="type">class</span> <span class="class">Before</span> {
    <span class="annotation">@Option</span>(names = <span class="string"><span class="delimiter">&quot;</span><span class="content">-u</span><span class="delimiter">&quot;</span></span>, type = {<span class="predefined-type">TimeUnit</span>.class, <span class="predefined-type">Long</span>.class})
    <span class="predefined-type">Map</span>&lt;<span class="predefined-type">TimeUnit</span>, <span class="predefined-type">Long</span>&gt; timeout;

    <span class="annotation">@Parameters</span>(type = <span class="predefined-type">File</span>.class)
    <span class="predefined-type">List</span>&lt;<span class="predefined-type">File</span>&gt; files;
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>从v2.0开始，<code>type</code> 属性不再是 <code>Collection</code> 和 <code>Map</code> 字段的必要属性：picocli将从泛型类型推断集合元素类型。
<code>type</code> 属性仍然像以前一样工作，只是在大多数情况下是可选的。</p>
</div>
<div class="paragraph">
<p>省略 <code>type</code> 属性会删除一些重复的内容，从而使代码更简洁、更清晰:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="java"><span class="type">class</span> <span class="class">Current</span> {
    <span class="annotation">@Option</span>(names = <span class="string"><span class="delimiter">&quot;</span><span class="content">-u</span><span class="delimiter">&quot;</span></span>)
    <span class="predefined-type">Map</span>&lt;<span class="predefined-type">TimeUnit</span>, <span class="predefined-type">Long</span>&gt; timeout;

    <span class="annotation">@Parameters</span>
    <span class="predefined-type">List</span>&lt;<span class="predefined-type">File</span>&gt; files;
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>在上面的示例中，picocli 2.0能够自动发现，命令行参数在添加到列表之前需要转换为 <code>File</code>，以及对于映射，需要将键转换为 <code>TimeUnit</code>，将值转换为 <code>Long</code> 。</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_自动帮助">自动帮助</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Picocli提供了许多便利方法，如 <code>run</code> 和 <code>call</code>，它们能够解析命令行参数、处理错误并调用接口方法来执行应用。</p>
</div>
<div class="paragraph">
<p>从此版本开始，当用户在命令行中指定一个注释有 <code>versionHelp</code> 或 <code>usageHelp</code> 属性的选项时，这些便利方法还将自动输出使用帮助和版本信息。</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="../images/AskingForHelp.jpg" alt="AskingForHelp"></span></p>
</div>
<div class="paragraph">
<p>下面的示例程序演示自动帮助:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="java"><span class="annotation">@Command</span>(version = <span class="string"><span class="delimiter">&quot;</span><span class="content">Help demo v1.2.3</span><span class="delimiter">&quot;</span></span>, header = <span class="string"><span class="delimiter">&quot;</span><span class="content">%nAutomatic Help Demo%n</span><span class="delimiter">&quot;</span></span>,
         description = <span class="string"><span class="delimiter">&quot;</span><span class="content">Prints usage help and version help when requested.%n</span><span class="delimiter">&quot;</span></span>)
<span class="type">class</span> <span class="class">AutomaticHelpDemo</span> <span class="directive">implements</span> <span class="predefined-type">Runnable</span> {

    <span class="annotation">@Option</span>(names = <span class="string"><span class="delimiter">&quot;</span><span class="content">--count</span><span class="delimiter">&quot;</span></span>, description = <span class="string"><span class="delimiter">&quot;</span><span class="content">The number of times to repeat.</span><span class="delimiter">&quot;</span></span>)
    <span class="type">int</span> count;

    <span class="annotation">@Option</span>(names = {<span class="string"><span class="delimiter">&quot;</span><span class="content">-h</span><span class="delimiter">&quot;</span></span>, <span class="string"><span class="delimiter">&quot;</span><span class="content">--help</span><span class="delimiter">&quot;</span></span>}, usageHelp = <span class="predefined-constant">true</span>,
            description = <span class="string"><span class="delimiter">&quot;</span><span class="content">Print usage help and exit.</span><span class="delimiter">&quot;</span></span>)
    <span class="type">boolean</span> usageHelpRequested;

    <span class="annotation">@Option</span>(names = {<span class="string"><span class="delimiter">&quot;</span><span class="content">-V</span><span class="delimiter">&quot;</span></span>, <span class="string"><span class="delimiter">&quot;</span><span class="content">--version</span><span class="delimiter">&quot;</span></span>}, versionHelp = <span class="predefined-constant">true</span>,
            description = <span class="string"><span class="delimiter">&quot;</span><span class="content">Print version information and exit.</span><span class="delimiter">&quot;</span></span>)
    <span class="type">boolean</span> versionHelpRequested;

    <span class="directive">public</span> <span class="type">void</span> run() {
        <span class="comment">// NOTE: code like below is no longer required:</span>
        <span class="comment">//</span>
        <span class="comment">// if (usageHelpRequested) {</span>
        <span class="comment">//     new CommandLine(this).usage(System.err);</span>
        <span class="comment">// } else if (versionHelpRequested) {</span>
        <span class="comment">//     new CommandLine(this).printVersionHelp(System.err);</span>
        <span class="comment">// } else { ... the business logic</span>

        <span class="keyword">for</span> (<span class="type">int</span> i = <span class="integer">0</span>; i &lt; count; i++) {
            <span class="predefined-type">System</span>.out.println(<span class="string"><span class="delimiter">&quot;</span><span class="content">Hello world</span><span class="delimiter">&quot;</span></span>);
        }
    }

    <span class="directive">public</span> <span class="directive">static</span> <span class="type">void</span> main(<span class="predefined-type">String</span>... args) {
        CommandLine.run(<span class="keyword">new</span> AutomaticHelpDemo(), <span class="predefined-type">System</span>.err, args);
    }
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>当使用 <code>-h</code> 或 <code>--help</code> 执行时，程序输出使用帮助：</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="../images/AutoHelpDemo-usage-screenshot.png" alt="自动帮助范例的使用帮助消息"></span></p>
</div>
<div class="paragraph">
<p>类似地，当使用 <code>-V</code> 或 <code>--version</code> 执行时，程序输出版本信息:</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="../images/AutoHelpDemo-version-screenshot.png" alt="自动帮助范例的版本信息"></span></p>
</div>
<div class="paragraph">
<p>自动输出帮助的方法：</p>
</div>
<div class="ulist">
<ul>
<li>
<p>CommandLine::call</p>
</li>
<li>
<p>CommandLine::run</p>
</li>
<li>
<p>CommandLine::parseWithHandler (通过内置Run&#8230;&#8203;​句柄)</p>
</li>
<li>
<p>CommandLine::parseWithHandlers (通过内置Run&#8230;&#8203;​句柄)</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>不自动输出帮助的方法:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>CommandLine::parse</p>
</li>
<li>
<p>CommandLine::populateCommand</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_更好的子命令支持">更好的子命令支持</h2>
<div class="sectionbody">
<div class="paragraph">
<p>此版本添加了新的 <code>CommandLine::parseWithHandler</code> 方法。这些方法提供了与 <code>run</code> 和 <code>call</code> 方法相同的易用性，但是对于嵌套的子命令有了更大的灵活性和更好的支持。</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="../images/strong_leadership.jpg" alt="strong leadership"></span></p>
</div>
<div class="paragraph">
<p>考虑具有子命令的应用需要做什么:</p>
</div>
<div class="olist arabic">
<ol class="arabic">
<li>
<p>解析命令行。</p>
</li>
<li>
<p>如果用户输入无效，则对解析失败处的子命令输出错误消息和使用帮助消息。</p>
</li>
<li>
<p>如果解析成功，则检查用户是否已请求顶层命令或子命令的使用帮助或版本信息。如果是，则输出请求的信息并退出。</p>
</li>
<li>
<p>否则，执行业务逻辑。通常这意味着执行最具体的子命令。</p>
</li>
</ol>
</div>
<div class="paragraph">
<p>Picocli提供了一些构造块来完成此任务，但是将它们连接在一起取决于应用。这种连接本质上是样板，且它在应用之间非常相似。例如，以前，具有子命令的应用通常包含如下代码:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="java"><span class="directive">public</span> <span class="directive">static</span> <span class="type">void</span> main(<span class="predefined-type">String</span>... args) {
    <span class="comment">// 1. parse the command line</span>
    CommandLine top = <span class="keyword">new</span> CommandLine(<span class="keyword">new</span> YourApp());
    <span class="predefined-type">List</span>&lt;CommandLine&gt; parsedCommands;
    <span class="keyword">try</span> {
        parsedCommands = top.parse(args);
    } <span class="keyword">catch</span> (ParameterException ex) {
        <span class="comment">// 2. handle incorrect user input for one of the subcommands</span>
        <span class="predefined-type">System</span>.err.println(ex.getMessage());
        ex.getCommandLine().usage(<span class="predefined-type">System</span>.err);
        <span class="keyword">return</span>;
    }
    <span class="comment">// 3. check if the user requested help</span>
    <span class="keyword">for</span> (CommandLine parsed : parsedCommands) {
        <span class="keyword">if</span> (parsed.isUsageHelpRequested()) {
            parsed.usage(<span class="predefined-type">System</span>.err);
            <span class="keyword">return</span>;
        } <span class="keyword">else</span> <span class="keyword">if</span> (parsed.isVersionHelpRequested()) {
            parsed.printVersionHelp(<span class="predefined-type">System</span>.err);
            <span class="keyword">return</span>;
        }
    }
    <span class="comment">// 4. execute the most specific subcommand</span>
    <span class="predefined-type">Object</span> last = parsedCommands.get(parsedCommands.size() - <span class="integer">1</span>).getCommand();
    <span class="keyword">if</span> (last <span class="keyword">instanceof</span> <span class="predefined-type">Runnable</span>) {
        ((<span class="predefined-type">Runnable</span>) last).run();
    } <span class="keyword">else</span> <span class="keyword">if</span> (last <span class="keyword">instanceof</span> <span class="predefined-type">Callable</span>) {
        <span class="predefined-type">Object</span> result = ((<span class="predefined-type">Callable</span>) last).call();
        <span class="comment">// ... do something with result</span>
    } <span class="keyword">else</span> {
        <span class="keyword">throw</span> <span class="keyword">new</span> <span class="exception">ExecutionException</span>(<span class="string"><span class="delimiter">&quot;</span><span class="content">Not a Runnable or Callable</span><span class="delimiter">&quot;</span></span>);
    }
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>这是相当大的样板代码量。Picocli 2.0提供了一种便利方法，它允许您将上述所有内容缩减为一行代码，这样您就可以专注于您应用的业务逻辑:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code data-lang="java"><span class="directive">public</span> <span class="directive">static</span> <span class="type">void</span> main(<span class="predefined-type">String</span>... args) {
    <span class="comment">// This handles all of the above in one line:</span>
    <span class="comment">// 1. parse the command line</span>
    <span class="comment">// 2. handle incorrect user input for one of the subcommands</span>
    <span class="comment">// 3. automatically print help if requested</span>
    <span class="comment">// 4. execute one or more subcommands</span>
    <span class="keyword">new</span> CommandLine(<span class="keyword">new</span> YourApp()).parseWithHandler(<span class="keyword">new</span> RunLast(), <span class="predefined-type">System</span>.err, args);
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>新的便利方法是 <code>parseWithHandler</code> 。您可以创建自己的自定义句柄或使用其中一个内置句柄。Picocli提供一些常见用例的句柄实现。</p>
</div>
<div class="paragraph">
<p>内置的句柄是 <code>RunFirst</code>、<code>RunLast</code> 和 <code>RunAll</code>。所有这些句柄都提供了自动帮助：如果用户请求usageHelp或versionHelp，
将输出所请求的信息，句柄将返回，而无需进一步处理。句柄希望所有命令都能执行 <code>java.lang.Runnable</code> 或 <code>java.util.concurrent.Callable</code>。</p>
</div>
<div class="ulist">
<ul>
<li>
<p><code>RunLast</code> 执行*最具体的*命令或子命令。例如,如果用户调用 <code>java Git commit -m "commit message"</code>，
那么picocli认为 <code>Git</code> 是顶层命令，<code>commit</code> 为子命令。在这个例子中，<code>commit</code> 子命令是最具体的命令，所以 <code>RunLast</code> 将只执行子命令。
如果没有子命令，将执行顶层命令。现在 <code>RunLast</code> 由Picocli内部用于执行现有的 <code>CommandLine::run</code> 和 <code>CommandLine::call</code> 的便利方法。</p>
</li>
<li>
<p><code>RunFirst</code> 只执行*首个*、顶层命令，并忽略子命令。</p>
</li>
<li>
<p><code>RunAll</code> 执行命令行中出现的*顶层命令和所有子命令。</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>还有一个 <code>parseWithHandlers</code> 方法，它与前面的方法类似，但额外允许您为不正确的用户输入指定一个自定义的句柄。</p>
</div>
<div class="sect2">
<h3 id="_改进的_run_和_call_方法">改进的 'run' 和 'call' 方法</h3>
<div class="paragraph">
<p><code>CommandLine::call</code> 和 <code>CommandLine::run</code> 便利方法现在支持子命令，并将执行用户指定的<strong>最后一个</strong>子命令。以前，子命令通常被忽略，只执行顶层命令。</p>
</div>
</div>
<div class="sect2">
<h3 id="_改进异常">改进异常</h3>
<div class="paragraph">
<p>最后，从此版本开始，所有picocli异常都提供了一个 <code>getCommandLine</code> 方法，
该方法返回解析或执行失败处的命令或子命令。
以前，如果用户对带有子命令的应用提供了无效的输入，那么很难准确地指出哪个子命令未能解析输入。</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_结论">结论</h2>
<div class="sectionbody">
<div class="paragraph">
<p>如果您已经在使用picocli，那么有必要升级v2.0。
如果您之前没有使用过picocli，我希望以上内容能让您有兴趣尝试一下。</p>
</div>
<div class="paragraph">
<p>其中许多改进源于用户反馈和随后的讨论。请不要犹豫，在picocli <a href="https://github.com/remkop/picocli/issues">问题跟踪器</a>上提出问题、请求添加新功能或提供其他反馈。</p>
</div>
<div class="paragraph">
<p>如果喜欢的话，请点击 <a href="https://github.com/remkop/picocli">GitHub项目</a>给我们星，并告诉您的朋友！</p>
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Last updated 2023-03-12 17:37:07 +0900
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